This invention relates to a thermal cut-off fuse which, in an electric appliance provided with a heat source, cuts off the electric circuit in the electric appliance when the ambient temperature of the electric appliance, because of abnormal generation of heat therein for some cause or other, rises beyond the rated service temperature zone and reaches the dangerous temperature zone, whereby the abnormal generation of heat is terminated with high responsivity.
In an ordinary thermal cut-off fuse, there is used a thermal pellet made of a thermosensitive material which retains a solid state at temperatures below a fixed level and which, when the ambient temperaure rises to reach the fixed level, melts into a liquid state with a fair loss of the volume occupied when the material was in a solid state. Further, this thermal cut-off fuse is provided inside its housing with a contact means for establishing electrical continuity between the two lead wires so that the contact means is kept in its closed state insofar as the thermal pellet retains its solid state and, when the pellet melts into a liquid state and loses its volume, this loss of the volume of the thermal pellet gives rise to an allowance of space for the contact means to release itself, by virtue of its own elasticity, from a restraining force exerted thereon, consequently open the contact and break the electrical continuity through the contact means.
In any of the conventional mechanisms for thermal cut-off fuses, once the electrical continuity between the two lead wires is broken, a space is simply left to intervence between the contact means and the portion of the opposed part to which the contact means was held in contact while the electrical continuity was still present. In other words, the contact means in effect is poised in mid air and, therefore, has a fair possibility of being readily swayed. When shocks are conveyed by chance to the electric appliance, the contact means which is supported to remain in its open state may possibly come into contact with some conductive material or causes the phenomenon of chattering to establish an accidental electrical continuity between the two lead wires.
An object of this invention is to provide a thermal cut-off fuse of high temperature-response accuracy, which once the ambient temperature rises to reach the fixed level of temperature rated for the electric appliance using the fuse and the fuse consequently breaks the electric circuit of the electric appliance, the fuse is not caused by external shocks or other impulses to produce an accidental electrical connection or an undersirable phenomenon such as chattering but maintains the broken state of electric continuity safely and, thus, provides highly reliable operation.